1. Field of the Invention
Embodiments of the present invention generally relate to a system and method of sensing an input object's position over a sensing region of a proximity sensing device.
2. Description of the Related Art
Input devices including proximity sensor devices, also commonly called touchpads or touch sensor devices, are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region, often demarked by a surface, in which the proximity sensor device determines the presence, location and/or motion of one or more input objects. Proximity sensor devices may be used to provide interfaces for the electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems (e.g., opaque touchpads integrated in, or peripheral to, notebooks or desktop computers). Proximity sensor devices are also often used in smaller computing systems (e.g., touch screens integrated in cellular phones).
Proximity sensor devices are typically used in combination with other supporting components, such as display or input devices found in the electronic or computing system. In some configurations, the proximity sensor devices are coupled to, or placed in close proximity to, these supporting components to provide a desired combined function or to provide a desirable complete device package. Many commercially available proximity sensor devices utilize one or more electrical techniques to determine the presence, location and/or motion of an input object, such as a capacitive or a resistive sensing technique. However, these useful electrical sensing techniques are susceptible to interference, such as electromagnetic interference (EMI), commonly generated by the other supporting components, such as liquid crystal display (LCD) components, that are position near the proximity sensor device. In touch screen type applications, since it is often desirable to have the proximity sensor information processed at a rate higher than the display refresh rate to better track the movement or position of an object, the EMI seen by each of the components in the proximity sensing device will vary at any instant in time, depending on where the display device is in its refresh cycle. The EMI seen by the proximity sensors thus tends to have a cyclical variation that is set by the display refresh rate (e.g., display frame rate) and its relation to the proximity sensing device's sensing rate (e.g., sensing frame rate), and thus is generally not random in nature. Current commercial electronic or computing systems have not been able to effectively minimize this type of EMI, and have commonly resorted to finding ways to minimize the magnitude of the interference by distancing the EMI generating components from the proximity sensing device, adding shielding components to the device package, and/or altering the display processing method, thus making the system more expensive and/or needlessly increasing the size of the complete system package. However, it is a common goal in the consumer and industrial electronics industries to reduce the cost and/or size of the electrical components in the formed electronic device.
Therefore, there is a need for a method and a system that has a proximity sensing device that is insensitive to the substantially non-random interference generated by other supporting components found in a desirably sized electronic system.